'84 Johnson 115 V4 lean sneeze?

emdsapmgr

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You are on to something. Let us know how it runs out this weekend. Good catch!
 

fmjnax

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I'm itching to try it out, but we've got two days of rain in the forecast so I have to wait. I am curious, though. Does such a minor amount of gumming on those tiny really cause that much grief to a motor?! The plug is a #34, which I understand to be 0.034" in diameter. With the gum, I would guess it was more like 0.01". Just seems like such a minute amount of air difference....
 

fmjnax

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Ok, ran another test. The motor now idles and won't die but it still sneezes. I pulled plug wires one at a time. The top left, as looking at it from the rear, may be the culprit. Pulling the wire makes the sneeze go away and spraying fuel into that throat smooths it out. No fuel spits out the carb throat so I know its not running rich. There are no apparent air leaks, as per my aerosol test around the motor. I pulled the plug immediately after the test and it looks perfectly fine (just as the other 3 do). Since it seems to be at least running, we are going to head to the lake in a bit. I've got some seafoam so we will see if a little minor decarb wont help. There's just something about that carb. I may go ahead and order a new one if I can't figure it out.
 

loiner1965

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Interesting reading.....fault finding is so frustrating and I hope you sort it out
 

fmjnax

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Haven't messed with the boat much, but have taken it out a few times. I have decarbed the motor TWICE now, and have been running SeaFoam in the the last 2 tanks of gas (half tank left of tank #2). I replaced the spark plugs after the 2nd decarb. It seems to have helped quite a bit. The sneeze has been minimized, but is still there.

It's probably going to be a couple of weeks before I can get the boat out again, so I think I may pull the carbs again, disassemble, and soak in a few different baths (carb cleaner, pinesol, other stuff I have read).
 

emdsapmgr

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Make sure both carb butterflys are seated completely closed when idling. If one is slightly ajar, that can mess thing up. No cam pressure on the carb roller, either.
 

fmjnax

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Thanks emdsapmgr. All butterflies seat completely and at idle there is a paper-width gap between the cam and roller, so no pressure on it. My gut feeling is that there is some sort of gumming in the low speed passage that carb cleaner and air just didn't get; thus why I am going to pull them and let them soak before I blow them out.
 

emdsapmgr

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Your concern for fuel delivery from the carbs is warranted. If one of the carb throats is running lean, not only is the engine short on fuel for that piston, it's also running with less oil.
 

fmjnax

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Time for another update. This may be lengthy, so bear with me. I haven't had a lot of boat time lately, but I finally got it back out on the water on Friday. Here's what I had done leading up to Friday and what happened on the water.

I pulled the carbs again and this time soaked them for a good 4-5 hours in B-12. I blew out the passages and noticed one of the high speed orifice plugs was partially gummed up. I removed the plug and reamed it out. Every other passage was perfectly clear and unobstructed. I blew them out with more aerosol carb cleaner and compressed air and inspected again; still clean. The carbs were then reinstalled.

As I was paying a closer eye to timing and the butterfly plates after reinstalling and moving the throttle level, I noticed two things:
- First, the lower butterflies were not sitting perfectly horizontal like the upper butterflies. They were off just enough that I could see the brass plate looking dead center. I adjusted the lower carb linkage so that the lower butterflies were in sync perfectly with the upper butterflies; both at idle and at WOT.

- Second, there was some play in the throttle cable.I noticed that when I moved the fast lever to full, there was a lag between when I moved the lever and when the spark advance at the engine moved. I also noticed that when I moved the fast lever down (off), the spark advance at the engine would not only lag, but it wouldn't completely back down either. I disconnected the throttle cable at the engine and noticed that the black boot over the cable has some play in it. I would imagine this means I need to replace it, but for now I have to make do with it. To try and rectify the issue, I found a barrel screw where the cable is held up on the carb spacer plate thing. Trial-and-error, I turned the barrel screw to minimize the amount of lag and dead space at the spark advance. I also adjusted the travel stop screws as applicable.


Now, fast forward a couple of weeks and we're ready to hit the water. I put the boat on the muffs in the drive way to make sure I didn't really muck it up. The fast lever was 100% better, but still not perfect (I'll probably do a little more adjusting on it). The engine fired up as well as it always has (fast lever about 75%, hold the choke, crank). Idle seemed ok. I gave a very quick bump of throttle just to confirm and it seemed ok.

The main problem and reason for this thread has been my lean sneeze and subsequent engine die. The engine did not die out this time. The sneeze was barely noticeable, but still there. The only time I ever had the sneeze problem was at idle. With the fast lever up or while on the throttle, it had never presented itself. I suspect that I may have just put a bandaid over the problem and have not really cured it. My thinking is that in adjusting the throttle cable at the engine, I increased the idle RPM's enough to drown out the sneeze. Unfortunately, the tachometer does not work so I don't currently have a way of measuring RPM's other than by ear. I did not notice a discernible increase in RPM's since prior the adjustment, however.

With the basic checks ok, I headed to the lake. The engine fired up just the same. Took the same amount of time to warm up before I could get off the trailer. It hopped up on plane quickly and reached the exact same top speed that I am used to. Every appeared perfectly usual. At idle, the sneeze was still nearly gone. The only time the motor died out was after idling for more than a few minutes. It seemed that the longer I idled, the more frequent it began sneezing. Brief idle was perfectly fine. I was even able to power-load the boat back on the trailer, where it used to just bog down and die.

Back home, I pulled the plugs and gave everything an inspection. All 4 plugs looked exactly the same and no indication of fouling or lack of lubrication. I ran 18 gallons of gas over the entire day and ran the boat hard. No overheating or smoking. Nothing indicates to me that a cylinder is dropping or lean on lubrication. I would have expected a blown powerhead otherwise.


So what is next on a list of things to check? Perhaps a bad/weak coil? I haven't completely checked spark yet, but the plugs are brand new and gapped .30. I know my charging system is working (if that even has anything to do with it). The fuel pump is in excellent condition and no sediment. Bulb and fuel lines seem ok. Carbs are completely cleaned. Reed valves are in excellent shape. Compression is good.
 

emdsapmgr

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It's possible the idle speed is too low. Since you don't have a tach, it's hard to tell. If it's too low, the engine can eventually slow, then not run right, then die out. Set the idle when the boat is floating normally in the lake. You can't set it on the trailer. When it's forward gear. Set it to 650-700 rpm's. You may be able to rent a timing light with a tach readout from a local auto parts store. Would be worth a day's rental just to confirm your idle rpms. Charging system is separate from the ignition. As you get your issues worked down to the final small ones, here's another thing to check: It's likely that your engine has a recirculation system on the intake manifold. When functioning correctly, it helps with idling. If you have one, make sure the brass one-way valves are functioning properly (or just replace them) and that the hoses are not cracked or leaking.
 

fmjnax

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Thank you emdsapmgr, you've been a huge help through this!

Where might I find the brass one-way valve on the recirc? There is a hose connected to the lower side of the metal air silencer bracket. Is it the other end of that hose, or something different?

*Edit*
Nevermind. I found them on the diagram. I'll check it out tonight and see how they are.
 
Last edited:

schematic

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Also check closely for double firing. use a timing light on the offending cylinder and watch for ghosting or double images on the flywheel.

Also....compression is not a "end all" of tests for engine condition. It is also possible that the offending cylinder has been damaged from fuel/oil deprivation and still shows reasonable compression.

This engine compression was within +- 10% compression but had unstable idle...
20140826_101804.jpg
 

fmjnax

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Thanks schematic. Is there any way of knowing for sure without pulling it all apart?
 

fmjnax

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I pulled the 4 valves (2 under each carb) and all 4 of them blow both ways. One of them is missing the screen behind it (and it's not in the socket). Looks like I will be replacing all 4 of them (at $30+ each! OUCH!).
 

fmjnax

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I decided to pop the wire screen off one to see how they work and a gooey rubber mess came out. Guess ethanol wrecked havok on them. Pulled the other two with the same results. Awesome...
 
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